1. Field of the Invention
The present invention relates generally to communications, and, more particularly, to a method and apparatus for generating comfort noise in a communications device, such as a cordless telephone.
2. Description of the Related Art
The telecommunications industry has undergone explosive growth over the past several years. A significant contribution to this growth has been the high demand for radio communication services, such as cordless telephone service, for example. Cordless telephones provide a greater flexibility to users than traditional landline phones by allowing them to move freely, not being tethered to the landline telephone system.
A typical cordless telephone system includes a handset unit and a base unit. The base unit is coupled to a telephone line and includes an antenna, a transmitter, and a receiver for communicating via radio frequencies with the handset unit. A local power line generally supplies the power for the base unit. The handset unit includes a speaker and a microphone, and also an antenna, a transmitter and a receiver for likewise communications with the base unit. Typically, the handset unit is powered by at least one battery. This battery is usually charged by the local power line when the handset unit is placed inside a cradle of the base unit.
The base and handset units generally communicate through transmission of digital signals. Typically, analog speech signals are digitized and coded before transmission. Speech signals are digitized because digitized signals are less susceptible to channel noise since they may be regenerated, as well as amplified, along the way, thereby reducing the possibility of being corrupted by the transmission system. On the receiving end, digitized signals are decoded and converted back to its analog form. A CODEC (CODing and DECoding device) commonly performs the coding/decoding functions, and sometimes analog-to-digital (A/D) and digital-to-analog (D/A) conversions. Since the base and handset units transmit, as well as receive signals, each unit typically includes a CODEC.
To achieve a greater bandwidth, cordless telephone systems employ voice compression algorithms. One popular voice compression algorithm is Adaptive Differential Pulse Code Modulation (ADPCM). The ADPCM scheme takes advantage of a high sample-to-sample correlation that exists in speech waveforms to reduce a transmission bit rate, while preserving an overall signal quality. In the ADPCM scheme, an analog voice signal is converted into digital representation and compressed into a lower bit stream through an encoding process for transmission.
Transmitted digitized, compressed signals, however, may not reach the intended destination error free. For example, a transmission from the base unit of the cordless telephone to the handset unit may include an error or errors such that quality of voice is jeopardized. Additionally, the transmission errors may introduce noise that result in undesirable sound, thereby causing discomfort to a listener on the receiving end.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a method is provided. The method includes receiving a signal, scaling the signal to a preselected value, indicating whether an error occurred during transmission of the signal, and providing the scaled signal as an output signal in response to an indication that the error occurred during transmission.
In another aspect of the present invention, an apparatus is provided. The apparatus includes a scaler for receiving a signal and being capable of scaling the signal to a preselected value. The apparatus includes an indicator capable of indicating that an error occurred during transmission of the signal, wherein the scaled signal is provided as an output signal in response to an indication that the error occurred during transmission.